Proper ligament engagement is an important topic of discussion for total knee arthroplasty; however, its importance to total ankle arthroplasty (TAA) is uncertain. Ligaments are often lengthened or repaired in order to achieve balance in TAA without an understanding of changes in clinical outcomes. Unconstrained designs increase ankle laxity,1 but little is known about ligament changes with constrained designs or throughout functional activity. To better understand the importance of ligament engagement, we first investigated the changes in distance between ligament insertions throughout stance with different TAA designs. We hypothesize that the distance between ligaments spanning the ankle joint would increase in specimens following TAA throughout stance. A validated method of measuring individual bone kinematics was performed on pilot specimens pre- and post-TAA using a six-degree-of-freedom robotic simulator with extrinsic muscle actuators and motion capture cameras (Figure 1).2 Reflective markers attached to surgical pins and radiopaque beads were rigidly fixed to the tibia, fibula, talus, calcaneus, and navicular for each specimen. TAAs were performed by a fellowship-trained foot and ankle surgeon on two specimens with separate designs implanted (Cadence & Salto Talaris; Integra LifeSciences; Plainsboro, NJ). Each specimen was CT-scanned after robotic simulations of stance pre- and post-TAA. Specimens were then dissected before a 3D-coordinate measuring device was used to digitize the ligament insertions and beads. Ligament insertions were registered onto the bone geometries within CT images using the digitized beads. Individual bone kinematics measured from motion capture were then used to record the point-to-point distance between centers of the ligament insertions throughout stance.INTRODUCTION
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